Re: [PATCH v4] gc: call "prune --expire 2.weeks.ago" by default

From: Wincent Colaiuta <win@wincent.com>
Date: Mar 13, 2008, 09:48 UTC
Message-ID: <7FB80115-C1E4-4F83-9374-41AB1BDA0579@wincent.com>
In-Reply-To: <7vod9j342h.fsf@gitster.siamese.dyndns.org>

El 13/3/2008, a las 0:39, Junio C Hamano escribió:

Show 15 quoted lines

> Ah,...
>
> But C language rules haven't changed in such a way that it  
> guarantees B to
> be evaluated before A when you write "A >= B", have it?
>
> So at least I think you would need something like this if you go that
> route:
>
>  		if (strcmp(value, "now")) {
>                	unsigned long now = approxidate("now");
>                	if (approxidate(value) >= now)
> 				return error("Invalid %s: '%s'", var, value);
> 			...
> 		}

Are you sure that that alternative provides any guarantees about evaluation order either? (I'm not a compiler expert, nor am I consulting a copy of the standard; but I don't think it does.)

In order to enforce evaluation in the required order I think it might have to be something like this:

	if (strcmp(value, "now")) {
		unsigned long now;
		if ((now = approxidate("now")) &&
		    approxidate(value) >= now)
			return error("Invalid %s: '%s'", var, value);
		...
	}

ie. the && operator guarantees left to right evaluation order, and since approxidate always returns a non-zero ulong the second expression (after the &&) will always be evaluated.

Cheers, Wincent